This is a renewal application for support of a stroke research program at the Massachusetts General Hospital, now in its third year of operation. During the first two years emphasis has been on the development and evaluation of methods to detect cerebrovascular disease in the symptomatic and asymptomatic groups by non-invasive approaches and in the development of non-invasive techniques for measurement of regional cerebral blood flow and metabolism. Further study and evaluation are needed to determine their usefulness in identifying patients with carotid disease who are at risk of stroke. These include the development of special instrumentation for 133Xe inhalation and the use of short-lived isotopes and the MGH positron camera to image the distribution f 13NH3 and H215O. Efforts will be made to measure regional cerebral oxygen consumption by this non-invasive method. The search for the ideal isotope will continue, and to this end the use of 127Xe, 85mKr and 81mKr, which appear to be ideally suited, will be explored. The study of the influence of collateral circulation and of induced hypotension on experimental cerebral infarction in primates will be carried out and the influence of therapeutic intervention on the incidence and size of the infarcted area will be evaluated. Studies will continue on the ideal method to achieve revascularization involving the use of special adhesive materials. Other investigations related to diagnosis have to do with the in vivo detection of thromboembolic cerebrovascular disease by technetium-labelled platelets. The study of aphasia will continue, with emphasis on pathoanatomic and behavioral aspects. The use of thin transverse, coronal and sagittal sections of the brain by use of a deconvolution technique applied to transverse axial computerized tomography will be utilized to enhance our ability to understand the pathoanatomic basis of aphasia in vivo. The initial development of a computerized stroke registry has turned out to be a real resource from which much correlative clinical information pertinent to our understanding of cerebrovascular disease is flowing, and expansion of this valuable activity is planned.